The Aluminum Extrusion Process

What is an Aluminum Extrusion?

Aluminum extrusion is used to create lengths of aluminum of a fixed cross-sectional profile. Through extrusion, very complex cross-sections can be created with excellent strength and surface finish. The process of aluminum extrusion works by forcing a block of metal, known as a billet, to pass through the die opening of smaller cross-sectional area than the billet itself.

Aluminum extrusion is widely used in construction, automobile and aircraft manufacture, industrial machinery and consumer goods.

The Extrusion Process

The extrusion process itself is a lot like the old Play-Doh Shape Maker. When you squeeze the Play-Doh through the press, the outcoming stream takes the shape of the selected mold. In the same way, the extruded aluminum takes the shape of the opening of the die. By using powerful hydraulic presses capable of exerting up to 15,000 tons of pressure, aluminum can be extruded into any shape you could imagine.

There are two main methods of aluminum extrusion:

• Direct Extrusion
• Indirect Extrusion

Direct Extrusion

Direct extrusion is the most important and widespread method used in aluminum extrusion. In direct extrusion, the die head is held stationary and the aluminum billet is forced through the die using a moving ram.

Direct extrusion is commonly used in the manufacture of solid rods, bars, and hollow tubes. The design of the die can be modified to produce a wide variety of solid and hollow profiles.

Indirect Extrusion

In direct extrusion, it is the billet that moves. In indirect extrusion, the aluminum billet is held stationary and the ram moves the die to exert pressure in the stationary billet. The advantage of keeping the billet stationary lies in keeping friction to a bare minimum.

Before extrusion starts, the cross-sectional shape is designed. The shape and features of the extruded metal are carefully calculated to maximize functionality, facilitate assembly, reduce weight, and minimize finishing costs. The unique characteristics of aluminum make it a cost-effective product with excellent functionality and a superb finish.

The Stages In The Aluminum Extrusion Process

1. A die is cast from the cross-section of the desired shape.
2. Aluminum billets are heated in a furnace until they reach 750-925ºF. At this point, the aluminum becomes a soft solid.
3. Lubrication, known as smut, is applied to the billet and ram. The smut is essential as it ensures the billet and ram do not stick together.
4. The ram applies pressure to the billet, pushing it through the die. During this process, liquid nitrogen is used to cool the die. The cooling prevents the formations of undesirable oxides, as well as prolonging the length of the die.
5. The extruded aluminum emerges from the die, taking on the same shape as the die opening. The extrusion is pulled onto a cooling table where it is exposed to air, water or a mixture of the two (depending on the final mechanical requirements of the metal).
6. Next a stretcher is applied. This corrects any twisting that may have occurred and straightens the metal. Hardness and strength are improved during the stretching process.
7. The extrusions – which may be 50 meters long – are fed to a saw conveyor and cut to the required profiles using a circular saw.
8. For some aluminum alloys, an artificial aging process is applied to achieve optimal strength. Artificial aging is accomplished via precipitation heat-treating in an aging oven. The aging process ensures the uniform precipitation of fine particles through the aluminum to enhance strength, hardness, and elasticity.
9. Finally, the finished profiles are taken to be finished or fabricated, ready to be shipped to the customer.

Benefits of Extruded Aluminum

Extruded aluminum has a number of advantages over other metals. There are metals which can match some of the desirable characteristics of aluminum, but no metal can match all these benefits at once.

The benefits of aluminum extrusions are many and include:

• Lightweight. Aluminum is around one-third of the weight of iron, steel, copper or brass. This makes it easier to handle and more economical to ship. For this reason, aluminum is widely used in automotive design, aerospace, and high-rise construction.
• Strong. The strength of aluminum is sufficient for all but the most demanding of applications. Aluminum is very suitable for cold environments, as it gets stronger as temperatures fall.
• Resistant to corrosion. Aluminum doesn’t rust. It is protected by a surface film of oxide, and this protection can be enhanced through anodizing.
• Excellent thermal conductivity. Aluminum conducts heat better than most metals. This makes it ideal for heat exchanger operations. Extrusion can be used to produce shapes optimal for thermal conduction.
• Affordable. The extrusion process is relatively inexpensive. Even prototypes can be made at a reasonable cost.